A shear thickening fluid, also known as a dilatant, is a non-Newtonian fluid that exhibits an increase in viscosity in response to an applied shear stress. In this class of fluids, the greater the magnitude of the applied stress, the more viscous the fluid becomes. In some cases, the stress response of the fluid causes that fluid to exhibit solid-like properties.
One of the common examples of such a fluid is a mixture of cornstarch and water. A mixture of cornstarch suspended in plain water creates a fluid having non-Newtonian characteristics and properties. Under normal conditions with minimal amounts of stress applied, the mixture acts as a fluid, exhibiting the traditional fluid-like characteristics, however, under increased amounts of stress, the mixture becomes more viscous and resisting the applied stress.
The stress response of a shear thickening fluid is completely passive, it does not require additional energy other than the force or stress imparted onto the fluid. An example application of a shear thickening fluid is the viscous coupling found in some automobile four-wheel drive systems. Rather than physically connecting two drive shafts, the drive shafts terminate in a shear thickening fluid filled unit, with each drive shaft having a set of closely space circular plates. Under normal driving, both the engine driven drive shaft and the free drive shaft rotate at the same speed since all wheels of the vehicle are rotating at the same speed. If the wheels attached to the free drive shaft begin to rotate slower due to slipping, the difference in rotational speeds between the driven and free drive shafts causes the shear thickening fluid to begin to thicken. The shear-thickened fluid effectively joins the two drive shafts, allowing power from the driven drive shaft to be transferred to the free drive shaft. This condition persists until the rotational speeds of the drive shafts is again matched after the slipping conditions have abated.
Current shear thickening fluids are used in situations like that described above. These situations typically only require that a fluid thickens at about a certain applied stress. The fluids are used in situations allowing for a certain level of inexactness, with the important characteristic being that the fluid thickens in response to an applied stress.
Therefore, the art could benefit from a shear thickening fluid in which the stress response characteristics can be controlled, such as the response of the fluid at various levels of applied stress.